As medical-use tomographic imaging devices for imaging a human body non-invasively, CT devices and MRI devices are widely utilized. Aiming at precision-enhancement in imaging and increasing the number of cases that are diagnosable, research and development have been carried out as to an element technology of a tomographic imaging device such as the CT device and MRI device. It is known that image reconstruction methods of the imaging device such as the CT device and MRI device fall into two broad categories, analytical reconstruction method and algebraic reconstruction method. Examples of the analytical reconstruction method are Fourier transform method, filtered back projection method, and convolution integral method. On the other hand, an example of the algebraic reconstruction method is an iterative reconstruction method.
In recent years, aiming at improvement of image quality, there have been actively suggested, methods that apply the iterative approximation method to an image reconstruction algorithm. For example, it is disclosed in the paragraphs 0005, and 0014 to 0019 of the patent document 1, describing a method that employs as the iterative approximation method (iterative method), an objective function (evaluation function) including a data fidelity term which enforces similarity between measured sinogram and a forward projection of an reconstruction image, and a regularization term which enforces a prior knowledge about a signal (e.g. smooth curved surface with sharp edges).